The goal of this project is to identify the genetic factors that predispose to canine narcolepsy. The first specific aim is to clone canarc-1, an autosomal recessive gene that produces canine narcolepsy. A very tight linkage marker for canarc-1 has been identified. This marker, a 0.85 kb band cross-hybridizing with a human p-switch Heavy- Chain immunoglobulin (Ig) probe (LOD score=13.6 at 0% recombination), has now been cloned and sequenced. Similar to the organization of Ig switch genes, it is composed of GC-rich 79-82 bp repeats and is 75% homologous to the human p-switch gene. We will use chromosome walking and Yeast Artificial Chromosome cloning techniques, together with corresponding studies in humans to identify the pathological gene. Narcoleptic dogs will then be used to study the gene functionally using in situ hybridization techniques and transgenic-related technologies. The second specific aim is to study the involvement of Dog Leucocyte Antigen (DLA) related genes in the canine pathology. Using Mixed Leucocyte Culture (MLC) techniques, we could not find any haplotype sharing in unrelated narcoleptic dogs. Recent experiments have shown that linkage disequilibrium between specific DR and DQ alleles is not very tight in dogs. Consequently, all our narcoleptic animals could share a common HLA DQ allele that would not have been detected using MLC. Alternatively all alleles carried could share a significant portion of their sequence. We will, therefore, clone and sequence the DQA1 and DQB1 alleles of a few narcoleptic dogs to test this hypothesis. This study should be facilitated by the fact that canine DQ sequences are now readily available. The third specific aim is to study Class Il expression in the brain of narcoleptic dogs. HLA antigens have been shown to be overexpressed in the brain of a number of immune pathologies, and we think this study could be very informative.